A wide variety of compounds for use as lubricating oil or fuel oil additives are known in this art. These include compounds variously referred to as pour point depressants, viscosity index improving compositions, wax crystal modifiers, and the like. In particular, Cashman et al, U.S. Pat. No. 2,825,717, discloses the preparation of certain lubricating oil additives by the copolymerization of polycarboxylic acid esters with other polymerizable monomeric materials, including vinyl compounds such as vinyl acetate. The preferred unsaturated polycarboxylic acid esters therein are fumaric acid esters produced from C.sub.1 through C.sub.18 aliphatic alcohols.
Bartlett, U.S. Pat. No. 2,618,602, discloses pour point depressing and/or viscosity index improving materials obtained by polymerizing certain specified alkyl fumarate esters. In particular this patentee discloses the use of polymerized fumarate esters of C.sub.12 to C.sub.14 alcohols for such purposes. This patent specifically discloses that the C.sub.12 alcohol was more effective than the C.sub.14 alcohol, although both polymerized esters exhibited pour point depressing properties.
Rossi et al, U.S. Pat. No. 4,088,589, discloses the use of specified mixtures of lubricating oil pour point depressants which include polyesters consisting of a polymeric ester of acrylic acid or methacrylic acid and a monohydric alcohol containing from 10 to 18 carbon atoms, and/or interpolymers of a vinyl alcohol ester of a C.sub.2 to C.sub.18 alkanoic acid (e.g., vinyl acetate) and a di(C.sub.6 -C.sub.18 alkyl) fumarate as one of the components thereof for improving the viscosity index of high wax content lubricating oils which also include viscosity index improving ethylene copolymers. Also, Wyman, U.S. Pat. No. 3,250,715, discloses terpolymers of dialkyl fumarates, vinyl esters, and alkyl vinyl ethers for improving the pour point of lubricating oils, and most particularly in which the dialkyl fumarates are prepared from various C.sub.10 through C.sub.18 alcohols including tetradecyl alcohol alone as well as alcohol mixtures averaging from 12 to 14 carbon atoms.
There has also been disclosed in co-pending U.S. patent applications Ser. Nos. 703,339 and 703,340, both of which were filed on Feb. 20, 1985, the use in various middle distillate fuel compositions for lowering the pour point and controlling the size of wax crystals in these products which specifically include polymers and copolymers of specific dialkyl fumarate vinyl acetate copolymers. Most specifically, these patent applications disclose the use of such compounds in which the average number of carbon atoms in the alkyl groups in the polymer or copolymer must be from 12 to 14. In addition these additives are also disclosed as being useful in combination with the polyoxyalkylene esters, ethers, esters/ethers and mixtures thereof, as well as with various other additives. Furthermore, British Pat. No. 2,023,645 discloses, for use in treating distillate fuel oils, various three-component systems which include as a first component flow improvers having an ethylene backbone, such as various ethylene polymers including ethylene polymerized with various mono- or diesters (e.g., vinyl acetate; and C.sub.13 fumarates), as a second component a lube oil pour depressant such as various oil soluble esters and/or higher olefin polymers (e.g., dialkyl fumarate, vinyl acetate copolymers), and as a third component various polar oil-soluble compounds (e.g., phenates, sulfonates, phosphates, and carboxylates).
It is also disclosed in Lewtas' U.S. Pat. Nos. 4,661,121 and 4,661,122 that the size of wax crystals forming in fuels boiling in the range of 120.degree. C. to 500.degree. C. can be controlled by an additive which includes the polymers and copolymers of mono- and di-n-alkyl esters of mono-ethylenically unsaturated C.sub.4 to C.sub.8 mono- or dicarboxylic acids, in which the average number of carbon atoms in the n-alkyl groups is from 14 to 18. These patents show a preference for copolymers of di-n-alkyl fumarates and vinyl acetate, and specifically state that the fumarates can be made from single alcohols or mixtures of alcohols, and when mixtures are used they are mixed prior to esterification. Furthermore, these patents disclose the use of various ethylene unsaturated ester copolymer flow improvers as co-additives therewith, but do not specify that these additives are produced from alcohol mixtures. Finally, in co-pending U.S. Ser. No. 944,545, filed on Dec. 19, 1986, which is a Divisional of U.S. Ser. No. 589,536, filed on Mar. 14, 1984, there is disclosed as a dewaxing aid a copolymer of dialkyl fumarate and vinyl acetate in which a large porportion of the alkyl groups are C.sub.20 to C.sub.24 alkyl groups.
While these various types of additive compositions have met with various degrees of success in the particular environments in which they are employed, it has been observed that various lubricating oil compositions, such as those containing certain viscosity improving additives, such as copolymers of ethylene and propylene, as well as those lubricating oil compositions containing lubricating oil flow improvers, nevertheless experience difficulty in passing recently adopted, more stringent, low temperature, slow cool performance tests designed to measure the low temperature pumpability of crankcase lubricating oils. It is therefore an object of the present invention to provide additives which enhance the low temperature pumpability of lubricating oil compositions.